Predicting the impacts of climate change on irrigated wheat yield in Fars province using APSIM model

Background and objectives: Over the last decade, climate change has been one of the most challenging issues in the scientific papers. Studying the impacts of climate change on crop productivity at regional scale will depend on the right estimate of future climate. This estimation is being implemented by climate models and most of them by general circulation models (GCMs). This study aims at predicting the future climate change impacts on wheat yield at six locations of Fars province.
Materials and methods: The current study was carried out at six locations including Abadeh, Darab, Eghlid, Fasa, Lar and Shiraz. Two general circulation models (HadCM3 and IPCM4) under three emission scenarios (B1, A1B and A2) for three periods (2011-30, 2046-65 and 2080-2099) were investigated for predicting future climate conditions in the study locations. LARS-WG software was used to generate daily climate parameters for each location. The daily climate data obtained from the outputs of LARS-WG were used as inputs for APSIM crop simulation model to simulate growth and development of wheat under future climate.
Results: The results showed that LARS-WG perfectly simulated radiation, minimum and maximum temperatures under future climate. However, the model performance was partly biased for precipitation compared with the other climate variables. According to the results obtained, the future minimum and maximum temperature in Fars will have an increasing trend. Compared to the baseline, the highest and lowest temperature rise will be occurred in Shiraz and Lar, respectively. In the current study, the higher grain yield during baseline period observed in Shiraz and Fasa (7753.95 and 7830.79 Kg/ha) and the lowest obtained in Lar (6810.62 Kg/ha). Compared to baseline period, the highest grain yield obtained in Eghlid and Abadeh (10761.17 and 10869.33 Kg/ha) in 2080-99 under A2 scenario. Averaging over emission scenarios, climate models and periods, the highest yield changes compared to the baseline was obtained in Eghlid (+12 to +43 percent) and Abadeh (+13 to +47 percent). In contrast, the lowest yield changes compared to the baseline was obtained in Darab (+11 to +18 percent) and Lar (+11 to +20 percent). Results of t-test also indicated that there was no significant difference between the climate models in terms of grain yield and other growth characteristics. Climate change increased grain yield and Leaf Area Index (LAI) and decreased length of growing season. Results of the current study showed that increasing of CO2 concentration in all locations was a major reason for increasing grain yield. Generally, the highest and lowest impact of climate change on wheat growth was observed in 2080-99 under A2 and in 2011-30 under B1, respectively.
Conclusion: Generally, the results revealed that wheat grain yield will have increasing trend in the future climate of Fars Province (from 12 to 24%). The increase in yield was a result of increasing both CO2 and temperature. However, positive effect of increasing CO2 was eliminated in some locations mainly due to increasing temperature more than optimal temperature of wheat.